1. Field of the Invention
The present invention relates to mechanical control mechanisms for conveyances. More particularly the present invention relates to a mechanical control mechanism for controlling application of the parking brake and for releasing the transmitting of power in conveyances such as electric wheelchairs.
2. Description of the Prior Art
Electric wheelchairs commonly have been adapted from manual wheelchairs by the addition of a battery, a pair of electric motors, a pair of mechanical drive mechanisms that connect the motors separately to left and right wheels, and an electrical control that controls the application of battery power separately and reversibly to the left and right wheels.
Further, prior art designs of electric wheelchairs commonly have included both mechanical mechanisms for separately releasing the mechanical transmitting of power from the electric motors to the wheels and separate parking brakes for each wheel.
Each mechanical drive mechanism commonly has included a reducing mechanism, such as a combination of a gear box and a pulley drive mechanism with the large pulley mounted on the wheel. The mechanisms for separately releasing the mechanical transmitting of power to the wheels commonly have been mechanisms for releasing belt tension. In some designs, a drive roller has been used to transmit power to the tire of the wheel; and releasing of power has been moving the drive roller away from the tire.
Separate parking brakes for left and right wheels commonly have been provided. Each parking brake has consisted of a toggle mechanism that includes both an actuating lever and a braking element. When the lever of one of the parking brakes is actuated to an over-center position, the braking element deformingly engages the resilient tire of that side of the wheelchair.
A degree of safety for occupants of electric wheelchairs, many of whom have lost some of their mental alertness, has been provided by dynamic braking; but this safety factor has not been a dependable one, as will be shown subsequently.
Dynamic braking commonly has been provided in electric wheelchairs as a natural result of poor mechanical efficiency of the mechanical drive mechanisms; but, more recently, in U.S. patent application Ser. No. 06/927,273, having a common inventor, electrical dynamic braking has been provided for wheelchairs that have mechanical drive mechanisms with good mechanical efficiencies.
Poor mechanical efficiency of mechanical drive mechanisms, which is even poorer when the wheels drive the electric motors, and the electrical dynamic braking of the aforesaid patent application, has protected occupants of electric wheelchairs from runaway conditions on slopes when changing from the parking mode to the electrically-propelled mode if the various mechanical controls have been positioned to leave the electric motors in driving engagement with the wheels when the mechanical brakes are released.
However, with prior art designs, it is possible to change from the parking mode to the electrically propelled mode by releasing the parking brake after the mechanical drives are engaged, or by releasing the parking brake before the mechanical drives are engaged. One order of actuation of the manual controls provides the safety of dynamic braking; and the other order invites harm to the occupant through a runaway wheelchair.
Further, in the stress of runaway conditions, and with the inertia thereof, a wheelchair may be overturned, and/or the occupant may be thrown from a wheelchair, by rapidly engaging the parking brake of one of the wheels. Therefore, it is important to reduce the danger of encountering runaway conditions.